Hi retiredbiker, I forgot but the css file only does the Preview window in Sigil. If you want to modify the scrollbars in the other windows, you need to attack the Qt with a qt_styles.qss file located in the same place as the CSS file.
I pinched a bit of code from Qt's website and added it to my qt_styles.qss file.
The first line was something I did a long time ago to ensure I had a white background in CodeView to improve some screenshots I was making. The rest is what I 'borrowed' from Qt's website.
Thanks, Turtle91, for the tip about 'Spoiler' and code pasting.